Dear Athulya,
Under promotions job vacancies in higher positions are filled by promoting selected lower level employees. Thus, Promotion is a vertical shifting of employees.
An important aspect of filling the job position through Promotion is that it motivates the existing employees to improve their efficiency and productivity and to apply for the promotions. However, if an employee has a surety of getting promoted, they may become lethargic towards the work and their efficiency may decrease.